The present invention relates to the folding of skelp or strip material to obtain a split tube, particularly of tubing having thin walls.
The forming of split tubes under utilization of a metal strip is, for example, carried out by means of suitable contour-rolling; see, for example, French Pat. No. 11,60,041.
Another method uses dies for forming such tubes; see, for instance, German Pat. No. 1,068,204.
German Pat. No. 597,120 describes a device for making tubes by drawing sheet stock over a mandrel and through a die. The tube's ends remain straight until forming has been completed.
Forming the strip into a tube without internal support and by drawing the strip from a coil is, for example, disclosed in U.S. Pat. No. 3,001,569.
German printed patent application No. P 28 05 735 discloses equipment for cold-forming a strip into a tube, and the joint is subsequently welded to obtain a longitudinal welding seam. This method is particularly applied to thick wall tubes which are drawn with internal as well as external support.
With the exception of this latter method, all others are disadvantaged by the fact that in the case of a thin-walled structure, the walls can easily wrinkle; particularly during formation of the round contour, folds can form in the wall.